1. Field of the Invention
The present invention relates to an apparatus for reproducing waveform data in a digital audio system.
2. Description of the Related Art
In a digital audio system such as CD (compact disk) and DAT (digital audio tape), preemphasis and deemphasis may be performed so as to improve sound qualities. Preemphasis implies that a gain of a signal in a frequency range with relatively low energy and a high audible sensitivity is previously increased and then the preemphasized signal is recorded. Deemphasis implies that the increased gain of this signal in that frequency range is decreased and then the signal with the original gain is reproduced. Levels of noise components contained in the above-described frequency range may be lowered by the preemphasis/deemphasis processing.
There are two different types of waveform data (i.e., digital signals indicative of recorded waveform signal) contained in digital audio data, namely emphasized data and non-emphasized data. As a consequence, conventionally the deemphasis process is carried out at the signal reproducing side in accordance with the following methods.
FIG. 2 is a schematic diagram for showing the first conventional reproducing apparatus. Both the waveform data "a2" and the selection signal "b2" are input into this reproducing apparatus. The data corresponding to the waveform data "a2" and the selection signal "b2" are contained in the digital audio data. After the waveform data "a2" has been digitally processed in the digital processing circuit 21, the digitally processed waveform data is D/A-converted in the D/A converter 22. In the case where the waveform data "a2" has been emphasis-processed, the switch circuit 23 is brought into the ON-state in response to the selection signal "b2", and the analog deemphasis processing is performed in the analog deemphasis circuit 24 to output the analog deemphasized waveform data. To the contrary, when the waveform data "a2" is not emphasis-processed, the switch circuit 23 is brought into the OFF-state in response to the selection signal "b2", so that this waveform data "a2" is output without executing the deemphasis process.
FIG. 3 is a schematic block diagram for representing the second conventional reproducing apparatus. The waveform data "a3" and the selection signal "b3" are input into the digital processing circuit 31. When the waveform data "a3" has been emphasis-processed, the data "c3" which is digitally deemphasis-processed in the digital deemphasis circuit 32 is supplied to the D/A converter 34. To the contrary, when the waveform data "a3" is not emphasis-processed the waveform data "a3" is supplied to the D/A converter 34 in response to the selection signal "b3". Either the waveform data "a3" or the waveform data "c3" is D/A-converted by the D/A converter 34 into the corresponding analog waveform signal which will then be output.
In the above-described first conventional reproducing apparatus, the switch circuit 23 is directly connected to the analog deemphasis circuit 24. As a consequence, in this first conventional reproducing apparatus, there is the problem that the sound quality is deteriorated due to the presence of switch circuit 23.
On the other hand, in the second conventional reproducing apparatus, after the waveform data is digitally deemphasis processed in the digital deemphasis circuit 32, the deemphasized waveform data is D/A-converted by the D/A converter 34. As a result, since the effect of the emphasis process is not given to the noise produced in the D/A converter 34, the sound quality is deteriorated.